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A DEVICE FOR COUNTING YOUNG FISH 

By Robert K. Robinson 

Superinietident U. S. Fisheries Stalion, White Sulphur Springs, W . Va. 

Paper presented before the Fourth International Fishery Congress 
held at Washington, U. S. A., September 22 to 26, 1908 

BULLETIN OF THE BUREAU OF FISHERIES : ; : : : : VOL. XX Vlll. P. 1001-1004 
Document No. 701 ::::::::::::::::;:;:: Issued April. 1910 



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APR 16 1910 



A DEVICE FOR COUNTING YOUNG FISH. 



By ROBERT K. ROBINSON, 
Superintendent U. S. Fisheries Station, White Sulphur Springs, II', Va. 



This device is intended as a means of measuring or counting young fish of a 
size from the fry stage up to the length of i % inches. The instrument is made 
of thin brass, nickel plated, and weighs about i pound. The 
cylindrical base is 4 inches in diameter and 4 inches high, 
with a top or neck which tapers to a diameter of iX inches, 
at which point is joined an upright tube of this diameter and 
15 inches long. The tube is enlarged at its upper end to 
form a funnel mouth. Immediately above the base, upon 
the sloping neck, is fastened a small metal tube, and to this 
is attached, by means of a short piece of small rubber tubing, 
a glass tube }i inch in diameter which extends up to the base 
of the funnel at the top and is held in place by wire clamps. 
Behind the glass tube, on the main tube of the apparatus, is 
engraved a 10- inch scale, graduated 10 points to the inch, 
beginning at zero at the bottom, and each fifth point above 
numbered consecutively to the top, or to 100 points. The 
lower end of the small metal tube is set in a shield- of metal, 
which is soldered to the sloping neck of the base of the vessel, 
this covered area of the latter being perforated to permit the 
entrance of water into the small tube while screening out the 
fish. Immediately below the zero point, and to the side of 
the scale, there is a small vent or valve, which is controlled 
by a spring lever and serves conveniently to adjust the water 
level in the apparatus to the zero point on the scale. The 
mode of using the apparatus may be understood by the fol- 
lowing directions: 

Fill the measure with water until the latter appears in 
the glass tube slightly above the zero point on the scale. By 
pressing the upper end of the valve lever the water may be 
allowed to escape and thus be easily adjusted to the zero 
point. 

Count out from any given lot of fish to be measured 300 
to soo of average size. Put the counted fish into the measure 




as free of water as possible; this may be done by putting Measure by means of « inch 
them into a quart graduate and, holding a small hand net 
tightly over the top of the graduate, draining the water off quickly by in- 
verting the graduate. A perforated dipper may serve in place of the hand net. 

1003 



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002 862 



602 



1004 BULLETIN OF THE BUREAU OF FISHERIES 



The displacement made by the counted fish will be shown by a rise of 
water in the glass tube above the zero point ; then by reading the number of 
points to which the water rises the average number of fish per point may be 
easily ascertained. To find the number of fish in an entire given lot, empty the 
measure, replace the water to the zero point, put the fish in by the operation 
above described, again read the number of points above zero, then multiply the 
latter by the number of fish per point, previously ascertained. 

The measure should be held perpendicular, which may be accomplished by 
suspending it between the thumb and index finger placed at the base of the 
funnel. 




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